When over-wintering black soldier fly larvae, a common question growers have is do black soldier flies die in winter? The answer is no, black soldier flies won't die in the winter, they only hibernate or go into sleeping mode. The larvae can survive at temperatures from 50-60F (10-15C). Lower temp below 20F (-6C) can kill them.

In the winter, you may see them stop moving vigorously and many get smaller in size. But when the weather warms up, they'll wake up, eat and get bigger again.

With this in mind, let's see some ideas to keep these guys warm during the winter.

#1. Food

When it's cold, we can make the foods for the larvae a bit more dry or thicker. Runny or watery foods, when exposed to the cool air, may turn cold. The cold liquid then can make the larvae cold when hanging around inside.

In the morning, we can feed them something a bit more moist. This is okay for the day. But at night when temperature drops, we'd want to thicken up the food so it acts as a kind of blanket to keep the grubs warm.

#2. Filtering Poop

People often screen out the grub castings from the feeding container to clean it & therefore make it less hot. But in the winter, to keep the warmth, you can leave the poop there without filtering. This adds to the bio-mass of the feed & helps a part in retaining the temperature.

#3. Feeding Box

It's good if you have the feeding box slightly elevated from the ground. Or more specifically, the box is not directly touch the ground.

This creates a sort of gap that acts as an insulation layer. It helps with the thermal balance at the base of the feeding box & creates some ventilation.

We can make four legs for the feeding box or use some rocks/bricks to lift it up a bit from the ground.

#4. Density

Increase the density of larvae inside one unit during the cold months. The larvae themselves are little heat generators. So keeping them near each other, with lots of them around, can help keep each one warmer.

#5. Lighting

If you have some lighting around to increase the temperature inside, then you can use it. The larvae don't like to see direct light when eating though. So keep some around for heating but not directly above the larvae.

You could use a cap to cover the larvae bucket to keep the light out. But there is still the warmth generated from the light source around to keep them warm. You could use a light bulb or artificial lighting for lighting.

Final Steps

If you're looking to store your larvae in the fridge, a wine fridge is your best bet. It will keep the larvae alive. The fridge we usually use at homes to store foods may be too cold for them.

To store the larvae, just put them in a Ziploc bag with some of the juice from the feeding box & pop them into the wine fridge. When it warms up, you can take them out again. Or feed them to the birds in the winter.

If you keep the larvae in a dry, dark, cool environment, they may be able to survive 6-8 months. If we want to wake them up again, then gradually introduce light back to them. Their bodies may then react to the warmth & kick-start the metabolism into full speed again.

Please note though during the winter some larvae may be motionless. If you see this, it does not mean that they are dead. It may be because of the cold & the larvae are just trying to conserve their energy by stopping any movements. Some growers may be too busy & don't feed these guys at all during this time. They won't die, you see, but they just grow much skinnier & smaller in size.

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